DESCRIPTION: This is a phase II research protocol to follow up their initial observations that serum free media could support osteoclast proliferation and differentiation. Specifically, the investigators propose to identify specific components required for osteoclast growth; determine the optimal correlation and concentration of each factor(s) and replace the serum containing or serum free media with chemically defined tissue culture components. These media will be used to assess the development of TRAP+ cells derived from murine bone marrow in a semisolid assay containing partially purified O-CSF. These studies will be performed at Washington University under the direction of Dr. M. Lee. Dr. Brown's laboratory will test various components including transferrin, insulin, cholesterol, other lipids, reducing agents and trace metals.